Tactile threshold of low-intensity focused ultrasound (LIFU) haptic devices has been defined as the minimum pressure required for tactile sensation. However, in contact-type LIFU haptic devices using an elastomer as a conductive medium, the tactile threshold is affected by the mechanical properties of the elastomer. Therefore, the tactile threshold needs to be redefined as a parameter that does not change with the mechanical properties of the elastomer. In this study, we used the LIFU haptic device to investigate the displacement of the elastomer surface at the tactile threshold while controlling the pulse duration, pulse repetition frequency, and pressure. We analyzed the displacement magnitude and rate to determine their relationship to the pressure. The displacement magnitude is the spatiotemporal peak of the displacement, and the displacement rate is the initial slope of the displacement at the starting point of LIFU pulse. The tactile threshold measured by the applied pressure showed the U-shaped graph, and the minimum pressure of 475 kPa at 2 ms and 407 kPa at 300 Hz was measured. The tactile threshold measured by the displacement show that the tactile sensation can be evoked at the small displacement magnitude (<3 μm) when the high displacement rate is present (>1.56 mm/s). Furthermore, the large displacement magnitude is required to induce the tactile sensation when the displacement rate is low. This result shows that the tactile threshold of a contact-type LIFU haptic device is affected by both the displacement magnitude and rate of the conductive medium. Our findings can be used as a guideline for developing a contact-type LIFU haptic device regardless of the elastomer used.

中文翻译：

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接触式低强度聚焦超声触觉装置中触觉位移的量化

低强度聚焦超声 (LIFU) 触觉设备的触觉阈值已被定义为触觉所需的最小压力。然而，在使用弹性体作为导电介质的接触式 LIFU 触觉设备中，触觉阈值受弹性体机械性能的影响。因此，触觉阈值需要重新定义为不随弹性体机械性能而变化的参数。在这项研究中，我们使用 LIFU 触觉设备来研究弹性体表面在触觉阈值处的位移，同时控制脉冲持续时间、脉冲重复频率和压力。我们分析了位移幅度和速率以确定它们与压力的关系。位移幅度是位移的时空峰值，位移速率是LIFU脉冲起始点位移的初始斜率。通过施加压力测得的触觉阈值呈U形图，测得的最小压力为2 ms时475 kPa和300 Hz时407 kPa。通过位移测量的触觉阈值表明，当存在高位移速率（> 1.56 mm / s）时，可以在小位移幅度（<3μm）下诱发触觉。此外，当位移速率较低时，需要较大的位移幅度来诱发触觉。该结果表明，接触式 LIFU 触觉设备的触觉阈值受导电介质位移幅度和速率的影响。